The invention relates to a method for deinking printed wastepaper, and the use of a deinking agent, to produce a recycled pulp that can be processed into paper products.
Wastepaper has long served as a source of raw material for use in papermaking, but typically, recycled wastepaper is used for making low grade paper and paperboard products. Today, as consumers have become more ecologically conscious, the demand for recycled content in higher-quality paper has increased. Because of its quantity, waste newsprint is a particularly important feedstock. It is necessary to remove the ink from these printed wastepapers so that it can be used in high quality products.
In a conventional wastepaper reclamation process, deinking methods include disintegrating the wastepaper, or "furnish", into a pulp or slurry in an aqueous alkaline deinking solution containing deinking agents, washing and then bleaching the pulp. Physical agitation of the paper fibers causes some ink separation. Caustic soda is usually used to provide the alkalinity needed to promote fiber swelling that results in the remaining ink to separate from the paper fibers. Surfactant is added to prevent the ink from reattaching to the fibers. The surfactant also acts as a foaming agent to carry off the ink when the fibers are washed in flotation cells. Hydrogen peroxide or other bleaching agents are added to whiten and brighten the pulp to the appropriate end-use requirements. Metal silicates are added to stabilize the bleaching agents.
The caustic soda and bleaching agents can have deleterious effects on the paper fibers. At the high pH levels needed for caustic soda to promote ink-fiber separation, the strong alkalinity can embrittle the fibers and cause alkaline darkening. Although the bleaching agents counteract the darkening, these agents can further weaken the fibers.
Therefore, there is a need for a wastepaper deinking process that reduces the amount of chemicals required, simplifies the process, and achieves brighter and more flexible fibers.